Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting downlink control information in a wireless communication system in which serving cells using different types of radio frames are aggregated.
Related Art
Long Term Evolution (LTE) based on 3rd Generation Partnership Project (3GPP) Technical Specification (TS) Release 8 is the leading next-generation mobile communication standard.
As disclosed in 3GPP TS 36.211 V8.7.0 (May 2009) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, in LTE, a physical channel can be divided into a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH), that is, downlink channels, and a Physical Uplink Shared Channel (PUSCH) and a Physical Uplink Control Channel (PUSCH), that is, uplink channels.
A PUCCH is an uplink control channel used to send uplink control information, such as a Hybrid Automatic Repeat reQuest (HARQ), an acknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel Quality Indicator (CQI), and a Scheduling Request (SR).
Meanwhile, 3GPP LTE-Advanced (A) that is the evolution of 3GPP LTE is in progress. Technology introduced into 3GPP LTE-A includes a carrier aggregation.
A carrier aggregation uses a plurality of component carriers. A component carrier is defined by the center frequency and a bandwidth. One downlink component carrier or a pair of an uplink component carrier and a downlink component carrier correspond to one cell. It can be said that a terminal being served using a plurality of downlink component carriers is being served from a plurality of serving cells.
Meanwhile, in the next-generation wireless communication system, a serving cell using time division duplex (TDD) and a serving cell using frequency division duplex (FDD) can be aggregated. That is, a plurality of serving cells using different types of radio frames can be allocated to a terminal.
Meanwhile, downlink control information has a predetermined format. That is, which fields are included in the downlink control information is predetermined, and the number of bits of each field is also predetermined. However, according to whether the same downlink control information format is used for TDD or for FDD, there is a field included or not included in the downlink control information format. Further, there is a field of which the number of bits varies depending on whether it is used for TDD/FDD even if the field is included irrespective of TDD/FDD.
How to effectively configure a format of downlink control information may be a matter to be considered in a wireless communication system in which serving cells using different radio frame structures are aggregated.